Biomedical subjects

J B Neaton

Publications and source records attributed to J B Neaton.

5 recordsLinked to original sources

PubMed2006

Renormalization of molecular electronic levels at metal-molecule interfaces.

The electronic structure of benzene on graphite (0001) is computed using the GW approximation for the electron self-energy. The benzene quasiparticle energy gap is predicted to be 7.2 eV on graphite, substantially reduced from its calculated gas-phase value of 10.5 eV. This decrease is caused by a change in electronic correlation energy, an effect completely absent from the corresponding Kohn-Sham gap. For weakly coupled molecules, this correlation energy change can be described as a surface polarization effect. A classical image potential model illustrates the impact for other conjugated molecules on graphite.

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PubMed2003

Epitaxial BiFeO3 multiferroic thin film heterostructures.

Enhancement of polarization and related properties in heteroepitaxially constrained thin films of the ferroelectromagnet, BiFeO3, is reported. Structure analysis indicates that the crystal structure of film is monoclinic in contrast to bulk, which is rhombohedral. The films display a room-temperature spontaneous polarization (50 to 60 microcoulombs per square centimeter) almost an order of magnitude higher than that of the bulk (6.1 microcoulombs per square centimeter). The observed enhancement is corroborated by first-principles calculations and found to originate from a high sensitivity of the polarization to small changes in lattice parameters. The films also exhibit enhanced thickness-dependent magnetism compared with the bulk. These enhanced and combined functional responses in thin film form present an opportunity to create and implement thin film devices that actively couple the magnetic and ferroelectric order parameters.

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PubMed2002

Low-energy linear structures in dense oxygen: implications for the epsilon phase.

Using density functional theory implemented within the generalized gradient approximation, a new nonmagnetic insulating ground state of solid oxygen is proposed and found to be energetically favored at pressures corresponding to the epsilon phase. The newly predicted static ground state is composed of linear herringbone-type chains of O2 molecules and has Cmcm symmetry (with an alternative monoclinic cell). Importantly, this phase supports IR-active zone-center phonons, and their computed frequencies are found to be in broad agreement with recent infrared absorption experiments.

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PubMed2002

Pressure amorphization through displacive disorder.

After classifying amorphous materials according to their topology, we review a recently proposed theory of pressure amorphization (PA) that arises from some degree of displacive disorder while retaining a crystalline topology. That theory is based on the notion that one or more branches of the phonon spectrum become soft and flat with increasing pressure and is illustrated by a simple model that possesses the range of features displayed by many of the materials which undergo PA with displacive disorder. We report the results of Langevin simulations of the simple model which show how the probability of amorphization increases with the number of unit cells in the system and support our theory. We comment on how to generalize the model for the study of real systems.

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PubMed2001

On the constitution of sodium at higher densities.

Using density functional theory the atomic and electronic structures of sodium are predicted to depart substantially from those expected of simple metals for r(s)<2.48 ( p>130 GPa). Newly predicted phases include those with low structural symmetry and semimetallic electronic properties (including zero-gap semiconducting limiting behavior), and even those that raise the possibility of superconductivity, all at currently achievable pressures. Important differences emerge between sodium and lithium at high densities, and these are attributable to corresponding differences in their respective cores.

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